HAO 2011 Profiles In Science: Dr. Liying Qian

Contact

Dr. Liying Qian is a Project Scientist I at the High Altitude Observatory at NCAR. Her specialty is in the use of upper atmospheric numerical models to study global changes in the coupled thermosphere/ionosphere system, including investigation of vertical coupling of the thermosphere/ionosphere and the lower atmosphere. She performs calculations of thermospheric neutral density for comparison with satellite drag data.

Publications

Figure 1: High resolution

(1) Qian, L., A. G. Burns, P. C. Chamberlin, and S. C. Solomon. 2011: Variability of thermosphere and ionosphere responses to solar flares, J. Geophys. Res., 116, A10309, doi:10.1029/2011JA016777.

Abstract: We investigated how flare characteristics affect the thermosphere and ionosphere responses to them. Model simulations showed that, for flares with the same magnitude and location, the thermosphere and ionosphere responses changed significantly as a function of flare rise and decay rates. The "Neupert Effect," which predicts that a faster flare rise time leads to a larger EUV enhancement during the impulsive phase, caused a larger maximum ion production enhancement. In addition, model simulations showed that increased E×B plasma transport due to conductivity increases during the flares caused a significant equatorial anomaly feature in the electron density enhancement in the F region, but a relatively weaker equatorial anomaly feature in TEC enhancement, due to dominant contributions by photochemical production and loss processes. The latitude dependence of the thermosphere response correlated well with the solar zenith angle effect, whereas the latitude dependence of the ionosphere response was more complex, due to plasma transport and the winter anomaly.

Figure 1 caption: Ionosphere responses to an X6.2 flare occurred on September 9, 2005. (a) NCAR TIME-GCM simulated enhancement of E×B at model pressure level lev=1.75; (b) The corresponding electron density enhancement at lev=1.75; (c) The corresponding TEC enhancement. 1 TECU is 10¹² electrons/cm²; (d) The corresponding enhancement of the sum of the ion production and loss at lev=1.75.

Changes of temperature and geopotential height

Figure 2: High resolution

(2) Qian, L., J. Lastovicka, R. G. Roble, and S. C. Solomon. 2011: Progress in observations and simulations of global change in the upper atmosphere, J.Geophys. Res., 116, A00H03, doi:10.1029/2010JA016317.

Abstract: Anthropogenic increases of greenhouse gases warm the troposphere but have a cooling effect in the middle and upper atmosphere. The steady increase of CO₂ is the dominant cause of upper atmosphere trends; other drivers are long-term changes of radiatively active trace gases such as CH₄, O₃, and H₂O, secular change of solar and geomagnetic activity, and evolution of the Earth's magnetic field. Observational and model studies have confirmed that in the past several decades, global cooling has occurred in the mesosphere and thermosphere; the cooling and contraction of the upper atmosphere has lowered the ionosphere and increased electron density in the E and F1 regions. Trends of other parameters, including the F2 region, mesospheric clouds, and mesopause wave activity, have been more controversial. Modeling investigations have demonstrated that both greenhouse gas forcing and secular change of the Earth's magnetic field can cause regional, diurnal, and seasonal variability of trends in F2 region density and height, which may contribute to discrepancies regarding ionospheric trends. Recent studies also may have reconciled discrepancies between space-based and ground-based observations of mesospheric clouds: both types of observations do not find statistically significant trends in the ~54°N to ~64°N latitude region, but space-based observations indicate that clouds may be increasing in frequency at higher latitude. Limited observational studies have suggested possible trends in wave activity. Changes in atmospheric dynamics, both as a consequence of global change in the lower and middle atmosphere and as a possible driver of trends in the upper atmosphere, is one of the critical open questions regarding trends in the upper atmosphere and ionosphere.

Figure 2 caption: Changes (double CO₂−base CO₂) of temperature and geopotential height due to doubling of CO₂, under geomagnetic quiet and equinoctial conditions, at 0000 UT, simulated by the NCAR TIME-GCM. (a) Zonal mean temperature change for solar minimum condition; (b) global mean temperature change for solar minimum (black) and solar maximum (red) conditions; (c) zonal mean geopotential height change for solar minimum condition; and (d) global mean geopotential height change for solar minimum condition. LN(P₀/P) is model pressure surface, where P is pressure at model surface and P₀ is a reference pressure of 5×10⁻⁴ mb.

Solar-rotational and annual/semiannual variations of neutral density

Figure 3: High resolution

(3) Qian, L. and S. C. Solomon. 2011: Thermospheric Density: An Overview of Temporal and Spatial Variations, Space Science Reviews, doi:10.1007/s11214-011-9810-z.

Abstract: Thermosphere neutral density shows complicated temporal and spatial variations driven by external forcing of the thermosphere/ionosphere system, internal dynamics, and thermosphere and ionosphere coupling. Temporal variations include abrupt changes with a time scale of minutes to hours, diurnal variation, multi-day variation, solar-rotational variation, annual/semiannual variation, solar-cycle variation, and long-term trends with a time scale of decades. Spatial variations include latitudinal and longitudinal variations, as well as variation with altitude. Atmospheric drag on satellites varies strongly as a function of thermospheric mass density. Errors in estimating density cause orbit prediction error, and impact satellite operations including accurate catalog maintenance, collision avoidance for manned and unmanned space flight, and re-entry prediction. In this paper, we summarize and discuss these density variations, their magnitudes, and their forcing mechanisms, using neutral density data sets and modeling results. The neutral density data sets include neutral density observed by the accelerometers onboard the Challenging Mini-satellite Payload (CHAMP), neutral density at satellite perigees, and global-mean neutral density derived from thousands of orbiting objects. Modeling results are from the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM), and from the NRLMSISE-00 empirical model.

Figure 3 caption: Solar-rotational and annual/semiannual variations of neutral density. (a) Global-mean neutral density at 400 km for 2003. Blue: daily density data derived from satellite drag; black: 81-day running mean of the daily density data; red: daily density simulated by NCAR TIE-GCM. (b) Global mean neutral density at 400 km for 2008. Blue: daily density data derived from satellite drag; black: 81-day running mean of the daily density data; red: daily density simulated by TIE-GCM. (c) F_10.7 and Ap indices for 2003. (d) F_10.7 and Ap indices for 2008.